An investigation into a perplexing outbreak among young kids in Cambodia is getting traction.

Doctors have identified a potential cause, a virus associated with hand, foot and mouth disease. (The illness is not foot-and-mouth disease, which affects only animals.)

In an update on the outbreak, the World Health Organization said there have been 59 cases of hospitalized young children since April. Fifty-two of the children died. An earlier estimate had put the death toll at 61.

Virologists found 15 of 24 samples from sick children tested positive for enterovirus 71, NPR's Anthony Kuhn reports from Singapore. But the investigators couldn't obtain samples in most of the cases because the children had already died, said a joint statement from WHO and the Cambodian health ministry.

Most of the Cambodian cases involved children under 3, who experienced high fevers, respiratory and neurological problems. The outbreak has hit children in Cambodia's southern and central provinces.

Kuhn reports this is believed to be the first known EV-71 outbreak in Cambodia. The disease has struck other parts of Asia. It has killed hundreds of children in China and Vietnam in the past two years.

But the form of the illness in Cambodia appears to have a higher fatality rate.

"Further investigation is ongoing and this includes the matching of the laboratory and epidemiological information," Cambodia's health minister H.E. Mam BunHeng said in the joint statement with WHO. "We hope to be able to conclude our investigation in the coming days."

Hand, food and mouth disease typically stats with fever, lack of appetite, malaise, and often a sore throat, WHO said. A day or so after the fever, painful sores show up in the mouth. They start as small red spots then become blistered and sometimes ulcerated. A rash on the hands or soles of the feet is also common a few days after the fever begins.

But, WHO said, someone with the illness may not develop the hallmark symptoms, or may have only have some, such as the rash or mouth ulcers.

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